Method of producing tin layers or tin alloy layers on copper or copper alloy wires by hot tin plating

ABSTRACT

THE INVENTION RELATES TO A METHOD AND A DEVICE FOR TIN PLATING COPPER JUMP WIRES. THE COPPER WIRE PASSES THROUGH A TIN BATH AND IS GUIDED THROUGH A STRIPPER NOZZLE, SITUATED A DISTANCE FROM THE BATH SURFACE. THE STRIPPER NOZZLE IS HEATED. THE BORE OF THE STRIPPER NOZZLE POSSESSES A WAVE SHAPED CROSS SECTION. FOR A WIRE DIAMETER OF 0.5 MM., 6 TO 20 HALF WAVES ARE PROVIDED AND THE DIAMETER OF THE BORES AS WELL AS THE DEPTH OF THE HALF WAVES ARE ADJUSTED TO THE DIAMETER OF THE WIRE. THE COPPER WIRES TIN PLATED ACCORDING TO THE INVENTION, HAVE A UNIFORM TIN LAYER WITH A THICKNESS &gt;3U AND ARE EXTREMELY SOLDERABLE. OUR INVENTION RELATES TO A METHOD OF PRODUCING TIN LAYER OR TIN ALLOY LAYERS ON COPPER OR COPPER ALLOY WIRES HAVING A DIAMETER OF &lt;0.5 MM. THE METHOD IS EFFECTED BY HOT TIN PLATING AT A UNIFORM THICKNESS OF &gt;3U ACROSS THE WIRE CIRCUMFERENCE. THE WIRE IS THEN PASSED THROUGH A TIN BATH OR A TIN ALLOY BATH AND IS UGUIDED THROUGH A PROFILED STRIPPER NOZZLE.

3,692,578 YERS EE Al RL E PNG OI CT RT MOO1 1 nited States Patent ficc 3,692,578 Patented Sept. l.9, 1972 3,692,578 NIETHOD OF PRODUCING TIN LAYERS OR TIN ALLOY LAYERS ON COPPER OR COPPER ALLOY WIRES BY HOT TLI PLATING Horst Schreiner and Henryk Fides, Nuremberg, Germany,

assignors to Siemens Aktiengesellschaft, Munich, Ber- Ein and Erlangen, Germany Filed Nov. 10, 1970, Ser. No. 88,400 Claims priority, application Germany, Nov. 13, 1969, P 19 57 031.1 Int. Cl. C23c 1/04 U.S. Cl. 117227 7 Claims ABSTRACT OF THE DISCLOSURE The invention relatos to a method and a device for tin plating copper jump wires. The copper wire passes through a tin bath and is guided through a stripper nozzle, situated a distance from the bath surface. The stripper nozzle is heated. The bore of the stripper nozzle possesses a wave shaped cross section. Por a wire diameter of 0.5 mm., 6 to 20 half waves are provided and the diameter of the hores as well as the depth of the half waves are adjusted to the diameter of the wire. The copper wires tin plated according to the invention, have a uniform tin layer with a thickness 3 ,u and are extremely solderable.

Our invention relatos to a method of producing tin layer or tin alloy layers on copper or copper alloy wires having a diameter of 0.5 mm. The method is effected by hot tin plating at a uniform thickness of 3 ,u across the wire circumference. The wire is then passed through a tin bath or a tin alloy bath and is guided through a profiled stripper nozzle.

For an impeccable solderability of thick tin plated copper jump wires, a minimum layer thickness of 3,u tin or tin alloys is required for each place of the wire. Various tin plating methods for producing copper jump wires have been suggested or made known, whose aim is to provide the copper wires with adhering, uniformly thick, good solderable tin layers. To this end, the copper wire may be appropriately treated, prior to its insertion into the tin bath, as well as following its emergence from the tin bath.

It is known, for example from German disclosure document 1,521,487, to produce a tin layer of medium thickness, between 3 and l on wires of copper or copper alloys. This is done by hot tin plating a tin layer placed upon a circular cross section wire during its passage through a stripper nozzle with polygonal cross section and to distribute the tin to a medium layer thickness that fiuctuates across the circumference of the wire but is uniform in the sectors. It is then formed immediately thereafter into a uniform layer thickness, with a calibrating nozzle of uniform cross section.

French Pat. 1,582,069 teaches placing a stripper nozzle with a bore of circular cross section, at such distance from the surface of the tin bath or of the bath, that said stripper nozzle lies just within the solidification region of the bath component.

The known method is afiiliated with shortcomings with respect to continuous manufacture. Above all, fluctuations in layer thickness occur and it is difiicult to adjust the layer thickness. It is an object of the invention to overcome these disadvantages.

The bore diameter of the stripper nozzle is bordered by a wave train, which runs between two concentric circles. The radii of the circles are adjusted to the radius of the wire and 3 to 15 half waves are provided for each millimeter of the circumference of the inner, concentric circles. A stripper nozzle may be used with 5 to 8 half waves per millimeter of the circumference.

The method of the invention provides tin plated copper jump wires With a tin layer of uniform thickness, across the entire circumference of the wire. The geometry of the profiled stripper nozzle prevents the Bernoulli effect, the so-called hydrodynamic pressure, which results in asymmetrical positions of the wire within the stripper nozzle when nozzles of circular cross section are employed. The resulting formation of sickle-shaped tin layers on the copper wire is avoided thereby. The selection of the wave level or height, that is the selection of the distance between the two concentric circles between which the wave train proceeds, determines the layer thickness. During the adjustment of the wire radius, the tolerance limits for the wire diameter should be taken into consideration. lt is preferred to heat the stripper nozzle. In a bath of pure tin and a bath temperature of 270 to 280 C., the stripper nozzle may be heated to 180 to 220 C., preferably to 200 C. In a bath comprising SnPb 40 and a bath temperature of 240 to 260 C., the nozzle may be heated to to 200 C. and preferably to 180 C. It should be stressed that compared to methods not using nozzles, wire velocities are obtainable, which are more than 0.2 m./ sec. In nozzle free methods such wire velocities result in tin layers, which are larger than 5 This means a high, uneconomical consumption of tin during the tin plating. The solderability of the copper wires tin plated according to the invention, may be tested according to the solder ball test. Testing conditions for a wire diameter of 0.5 mm., are a solder ball weight of 75 mg. when SnPb 40 is used as solder and a testing temperature of 235 C. The clamped wire is dipped into a liquid solder pearl and the time which elapses until the solder drop encloses the entire wire is measured. In wires which are tin plated according to the invention the solder periods are consider ably below a second, even if changes have taken place for many days, for example by tempering. Due to this good solderability, the copper wires tin plated according to the invention are also suitable for automatic soldering processes such as for example sonic or immersion welding.

A preferred device for performing the method of the invention is provided with a stripping nozzle, where the radius of the inner one of the concentrc circles, wherebetween the wave train proceeds is 0.5 to 2.5;4 larger than the upper tolerance limit for the radius of the wire. Preferably, a stripper nozzle is provided where the difference between the radii of the inner and the outer one of the concentric circles, wherebetween the wave train proceeds, is 10 to 50,u, preferably 20 to 30u.

The half waves of the wave train which contact the outer of the concentric circles may be shaped at least nearly as a circular aro. The stripper nozzle may consist of diamond, ruby, hard metal or stainless steel.

The distance between the bath surface and the nozzle should lie within the solidification range of the tin or the tin alloy. The distance rangos from 200 to 1200 mm., and is preferably from 600 to 800 mm.

FIG. 1 is a schematic illustration of a thick tin plating installation;

FIG. 2 is a stripper nozzle; and

FIG. 3 is an enlarged section of the stripper nozzle of FIG. 2.

The invention will be further described with references to FIGS. 1 to 3.

FIG. 1 schematically illustrates a thick tin platng installation. The copper jump wire 1 is removed from reel 2, in the direction shown by the arrows. After two deflection rollers, the wire passes first in an annealing furnace 3, through a water vapor atmosphere, at 800 to 900 C., where its surface is purified. Thereafter, the wire 1 enters a water bath 4. Following the water bath, the

water is stripped off the wire surface with the aid of a drying brush 5. The copper wire passes through an etchant solution section (HCl acid) 6 to remove surface layers, and enters the tin bath 7. The HCl etchant section consists of a dropping vessel, filled with hydrochloric acid. The dropping vessel is situated above strippers which may be produced of felt. The felt strips are saturated with hydrochloric acid, with the aid of the dropping vessel.

In the tin bath 7, the wire 1 is deflected With a defiection roller 8 and leaves the tin bath at least nearly vertically. The tin bath 7 is covered with charcoal 9, at least in the region of the inlet point of the wire I, in order to prevent contaminaton of the tin bath 7, for exmple, an oxidation of the tin surface. The tin bath is covered in the location of the outlet point of the wire with an oil layer 10.

The copper wire 1, which emerges from the tin bath 7, is guided through a stripper nozzle 11, which is a distance l over the tin bath 7. The excess tin is removed from the Wire 1 by the stripper nozzle 11. The wire, after passing a cooling path 12, is deflected va rollers 13 and 14 and guided to a take up device, not illustrated in FIG. 1.

The stripper nozzle has a bore with a wave profile. The inner diameter of the bore and the depth of the waves are adjusted to the diameter of the copper wire. This adjustment will be derived from subsequent descriptions of the figures. The stripper nozzle is heated and spaced a distance l over the surface of the tin bath 7, which in known manner is Within the incipient solidification point of the tin or tin alloy bath, With a wire pay out speed of greater than 1 m./sec., the distance l is between 200 and 1200 mm. and preferably between 600 and 800 mm. A device for heating the nozzle or die 11 is not shown in FIG. l, in order to preserve clarity. The nozzle can be heated electrically, for example, by an nductive coil. It is favorable with a tin bath having a temperature between 270 and 280 C., for the stripper nozzle or die 11 to have a temperature from 180 to 220 C. and preferably 200 C., with an SnPb 40 bath having a temperature between 240 and 260 C. for the nozzle to have a temperature of 160 to 200 C., preferably 180 C.

FIG. 2 illustrates a section through a stripper nozzle 11, with a copper wire 1 also shown in section in the bore 15 of the stripper nozzle. The bore 15 of the stripper nozzle 11 has a wave profile. In FIG. 2, two concentrc circles 16 and 17 are shown with radii R and R The closed wave train 18 runs between the concentric circles 16 and 17. The wave train 18 has between 3.5 and 15, and preferably to 8 half waves, per millimeter of the circumference of the inner circle 16. FIG. 2 shows a nozzle for a wire radius R of 0.25 mm. A closed wave train with 8 half waves is provided, this corresponds to at least 5 half waves relative to a unit length. The radi R and R and thus the depth (R R of the half waves of the wave train 18 are adjusted to the radius R of the wire. Determining this adjustment are the tolerance limits for the wire radius R and the desired layer thickness for the tin plating. The tolerance limits for the wire radius R enter essentially in the radius R of the interior concentric circle 16. The radius must be selected at least large enough so as to prevent, during the passage of the wire 1, the wave profile from being embedded in the wire surface. It is preferred that R is 0.5 and 2.5,u greater than the upper tolerance limit for the wire radius R The layer thickness is essentially determined by the depth R -R of the individual waves and by the distance between the wave maximum and minimum.

FIG. 3 illustrates an enlarged section of the stripper nozzle lt) according to FIG. 2 and shows that the half waves 18a, which touch the outer concentric circle 17, are preferably shaped at least nearly as a semicircle. The radius r of a circle 19 drawn into a half wave 18a and the chord c which is defined by the intersecting points of the circle 19 with the inner concentric circle 16, are decisive for the layer thickness, next to the difference between the radii R and R of the concentric circles 16 and 17. The radius r or the length of the chord c is determined by the number of half waves of the wave train 18. It Was found that for a layer thickness which ranges between 3/L and about 7p., the number of half waves per millimeter of the circumference of the circle 16 must be between 3.5 and 15. The difierence R R between the radii R, and R of the concentric circles 16 and 17 may vary between 10 and 50y., preferably from 20 to 30 The tin layer adhering to the wire is profiled with a thus dimensioned stripper nozzle. The subsequent smoothening is etected by itself through the surface tension of the profiled tin layer, whereby the form of profiling provides a uniform, average layer thickness of at least almost constant size, over the entire wire circumference. This provides the aforedescribed advantages and the excellent solder characteristics of the copper jump wire tin plated in accordance with the method of the invention,

Stripper nozzle 11 is made of diamond, ruby, hard metal or stainless steel, in order to obtain the best possible stability therefor. The stripper nozzle of the invention is produced from a stripper nozzle with a circular bore whose diameter is 2R To produce a stripper nozzle according to FIG. 2 with 8 half waves for a wire radius R of 0.25 mm., the nozzle is clamped into an octagonal holder and a tungsten wire with radius r is threaded through the bore of the nozzle and moved back and forth in exact guidance. The grinding material may be a diamond board. The processing is carried out in steps and the wave depth is measured by microscope. After a half wave is ground out, the clamping device is placed upon the next polygonal surface so that one by one, all half waves shaped in a circular arc are worked in. The sharp edges are subsequently rounded ol by after-polishing. For instance when a 0.500 mm. thick copper wire with tolerance limits between 0.497 and 0.508 mm. is to be tin plated, the profiled nozzle 11 having 8 half waves is dimensioned as follows: radius R 0.259 mm.; radius R 0.284 mm. The copper jump wire had a pay out velocity of l m./ sec. A uniform tin layer thickness of 5,a was obtained over the entire wire circumference and the wire length and the temperature of the stripper nozzle Was 200 C. The distance of the profiled nozzle from the surface of the bath was between 600 and 800 mm. There was a uniform tin layer thickness as was determined by galvanic removal and light optical measurements of the cross section. The tin layer thickness was measured between 5 and 6.5,u.

German disclosure document 1,521,487, corresponds to U.S. application Ser, No. 605,743, filed Dec. 29, 1966 and now abandoned, while French Pat. 1,582,069 corresponds to U.S. application Ser. No. 724,012, filed Apr. 25, 1968, now Pat. No. 3,579,377.

What is claimed is:

1. A method of producing tin layers or tin alloy layers upon copper or copper alloy wires by hot tin plating with a uniform thickness 3u along the wire circumference, wherein the wire passes through a tin bath or tin alloy bath and is guided through a profiled stripper nozzle arranged 200 to 1200 mm. above the bath surface, said stripper nozzle has a bore whose cross section is limited by a wave train, said wave train proceeds between two concentric circles, the radius of the inner of said concentric circles is from 0.5 to 2.5,u greater than the outer tolerance of the radius of the wire to be hot tin plated, the diflerence between the radi of the inner and the outer of the two concentric circles between which the wave train runs is from 10 to 50 and approximately 3.5 to 15 half waves are provided for each millimeter of the circumference of the inner of said concentric circles.

2. The process of claim l, wherein the stripper nozzle has from 5 to 8 half waves per millimeter of circumference.

3. The process of claim l, wherein the stripper nozzle is heated.

4. The process of claim 3, wherein a bath tempera 3,385,259 5/1968 Orban et al. 117102 M UX ture of 270 to 280 C. is used for a pure tin bath and 3,540,918 11/1970 Trattner et al. 117102 M the stripper nozzle is heated to 180 to 220 C. 3,579,377 5/1971 Schreiner et al. 117102 M X S. The process of claim 4, wherein the stripper nozzle 1,890,292 12/1932 Hinsky 117102 L X is heated to 200 C. 5 1,994,802 3/1935 Adams 117128 X 6. The process of claim 3, wherein a bath tempera- 2,036,048 3/ 1936 Hinsky 118125 ture of 240 to 260 C. is used for SnPb 40 and the strip- 2,328,096 8/1943 Reevely 117102 L X per nozzle is heated to 160 to 200 C. 3,402,696 9/1968 Richards 118125 7. The process of claim 6, wherein the stripper nozzle i h d to 180 c, 10 ALFRED L. LEAVI'II, Primary Examiner I. R. BATTEN, JR., Assistant Examiner References Cted UNITED STATES PATENTS U.S. Cl. X.R.

1,551,751 9/1925 Kozak 117 114 B UX 117102 M, 114 B, 12s, 231; 118-125 2,515,022 7/1950 Snyder et al. 117114B 15 

